{"id":31714,"date":"2023-06-11T11:19:39","date_gmt":"2023-06-11T09:19:39","guid":{"rendered":"https:\/\/yuboost.com\/quels-sont-les-effets-indesirables-de-la-vitamine-c\/"},"modified":"2026-09-29T13:43:21","modified_gmt":"2026-09-29T11:43:21","slug":"what-are-the-side-effects-of-vitamin-c","status":"publish","type":"post","link":"https:\/\/yuboost.com\/en\/expertise\/what-are-the-side-effects-of-vitamin-c\/","title":{"rendered":"What are the side effects of vitamin C?"},"content":{"rendered":"<div>\n<style>\n  \/* Sans effet visible sur desktop *\/\n  .yb-art-layout > *{min-width:0;}\n  .yb-art-body{min-width:0;}\n  .yb-art-body img{max-width:100%;height:auto;}\n  .yb-art-tablewrap{max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch;}<\/p>\n<p>  @media (max-width:900px){\n    .yb-art, .yb-art *{box-sizing:border-box;}\n    .yb-art{max-width:100%;overflow-x:hidden;}\n    .yb-art-body{max-width:100%;overflow-wrap:break-word;}\n    .yb-art-table{min-width:560px;}\n    .yb-art-layout{display:block !important;grid-template-columns:minmax(0,1fr) !important;}\n    .yb-art-aside{position:static !important;width:100% !important;margin-top:32px;}\n  }<\/p>\n<p>  @media (max-width:600px){\n    .yb-art-container{padding-left:18px !important;padding-right:18px !important;width:100% !important;max-width:100% !important;}\n    .yb-art-hero,\n    .yb-art-key,\n    .yb-art-quote,\n    .yb-art-cta{max-width:100% !important;width:100% !important;margin-left:0 !important;margin-right:0 !important;}\n    .yb-art-hero-in,\n    .yb-art-cta-in{padding-left:20px !important;padding-right:20px !important;}\n    .yb-art-hero h1{font-size:clamp(26px,7vw,34px);line-height:1.2;}\n    .yb-art-meta{flex-wrap:wrap;gap:6px;}\n    .yb-art-cta-btns{flex-direction:column;align-items:stretch;}\n    .yb-art-cta-btns > a{text-align:center;}\n  }\n<\/style>\n<div class=\"yb-art\">\n<div class=\"yb-art-container\">\n<nav class=\"yb-art-crumb\"><a href=\"\/en\/\">Home<\/a> \u203a <a href=\"https:\/\/yuboost.com\/en\/our-articles\/\">Our articles<\/a> \u203a <span>Vitamin C side effects<\/span><\/nav>\n<div class=\"yb-art-hero\">\n<div class=\"yb-art-hero-blob\"><\/div>\n<div class=\"yb-art-hero-in\">\n        <span class=\"yb-art-eyebrow\">Vitamins &amp; safety<\/span><\/p>\n<h1>Vitamin C <span class=\"yb-art-accent\">side effects<\/span>, overdose and contraindications<\/h1>\n<p class=\"yb-art-hero-sub\">1,000 mg tablets, effervescents, liposomal vitamin C, high-dose infusions: which side effects of vitamin C are real, from what dose, and who should avoid it. A review based on the MSD Manual, EFSA, ANSES and published medical research.<\/p>\n<div class=\"yb-art-meta\">\n          <img decoding=\"async\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\" alt=\"Dr Alexandra Miles\"><br \/>\n          <span>By <strong>Dr Alexandra Miles<\/strong><\/span><br \/>\n          <span>\u2022<\/span><span>Reviewed September 2026<\/span><br \/>\n          <span>\u2022<\/span><span>15 min read<\/span>\n        <\/div>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"yb-art-layout\">\n<div class=\"yb-art-body\">\n<p>Vitamin C, or ascorbic acid, is the most widely taken vitamin supplement. It is water-soluble, the body stores very little of it and passes the excess out in the urine. That is what has earned it its reputation as a &#8220;harmless&#8221; vitamin. The reputation is largely deserved at dietary doses. It holds up less well with 1,000 mg tablets taken every day, effervescents taken by someone with high blood pressure, or infusions of several grams. <strong>Vitamin C side effects<\/strong> do exist. They depend on the dose, on the form, and above all on the person taking it. Here is what the data show, and what should make you measure before you supplement.<\/p>\n<div class=\"yb-art-key\">\n<div class=\"yb-art-key-t\">Key takeaways<\/div>\n<p>From food alone, no vitamin C overdose has ever been described. With supplements, the MSD Manual puts the upper limit at <strong>2,000 mg a day<\/strong>: above it, nausea and diarrhoea are the most common <strong>side effects of vitamin C<\/strong>. The risk that really matters is renal: part of the vitamin C you take is converted into <strong>oxalate<\/strong>, which promotes <strong>kidney stones<\/strong> and, at very high doses, kidney damage. Two contraindications are firm: iron overload (haemochromatosis, thalassaemia) and, for high-dose infusions, <strong>G6PD deficiency<\/strong>. Effervescent tablets add sodium, a problem if your blood pressure is high. Before any long-term supplementation or any infusion, a <a href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/\">blood test<\/a> measures your kidney function, blood sugar and blood count, <strong>at home and with no prescription needed<\/strong>.<\/p>\n<\/p><\/div>\n<h2>Vitamin C: daily needs and the safety limit<\/h2>\n<p>Two figures frame vitamin C. On one side, the <strong>reference intake<\/strong>, the amount that covers the needs of a healthy adult. On the other, the <strong>tolerable upper intake level<\/strong> (UL), the total daily dose above which a risk of adverse effects can no longer be ruled out.<\/p>\n<p>For the reference intake, the French food safety agency ANSES sets <strong>110 mg a day<\/strong> for adults, 120 mg during pregnancy and 170 mg while breastfeeding. The MSD Manual quotes the US values, 75 mg for women and 90 mg for men, and adds that smokers need <strong>an extra 35 mg<\/strong> a day. One kiwi, one pepper or two oranges are enough to reach those amounts.<\/p>\n<p>For the upper limit, the situation is unusual. In its 2024 summary of tolerable upper intake levels, the European Food Safety Authority (EFSA) states for vitamin C: <strong>no adequate data to derive a UL<\/strong>. That is not a green light. It means no precise toxicity threshold could be set for lack of suitable studies, even though digestive effects and a risk of stones are documented. The US authorities, cited by the MSD Manual, set a practical limit at <strong>2,000 mg a day<\/strong>. That is the figure we use as our benchmark.<\/p>\n<div class=\"yb-art-tablewrap\">\n<table class=\"yb-art-table\">\n<thead>\n<tr>\n<th>Benchmark<\/th>\n<th>Adult value<\/th>\n<th>Source<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Reference intake<\/td>\n<td><strong>110 mg\/day<\/strong> (120 mg pregnancy, 170 mg breastfeeding)<\/td>\n<td>ANSES<\/td>\n<\/tr>\n<tr>\n<td>Recommended intake (US values)<\/td>\n<td>75 mg women \/ 90 mg men, + 35 mg for smokers<\/td>\n<td>MSD Manual<\/td>\n<\/tr>\n<tr>\n<td>European upper limit<\/td>\n<td>Not set (insufficient data)<\/td>\n<td>EFSA 2024<\/td>\n<\/tr>\n<tr>\n<td>Practical upper limit<\/td>\n<td><strong>2,000 mg\/day<\/strong>, above it nausea and diarrhoea<\/td>\n<td>MSD Manual<\/td>\n<\/tr>\n<tr>\n<td>Blood level defining deficiency<\/td>\n<td>&lt; 0.2 mg\/dL (&lt; 11 \u00b5mol\/L)<\/td>\n<td>MSD Manual<\/td>\n<\/tr>\n<tr>\n<td>Standard pharmacy tablet<\/td>\n<td>500 to 1,000 mg, i.e. 5 to 9 times the reference intake<\/td>\n<td>Product labels<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<p class=\"yb-art-sources\">The Swiss reference values are published by the <a href=\"https:\/\/www.sge-ssn.ch\/de\/empfehlungen\/naehrstoffe-lebensmittel\/referenzwerte\/\" target=\"_blank\" rel=\"nofollow noopener\">Swiss Society for Nutrition<\/a> and the Federal Food Safety and Veterinary Office, based on the D-A-CH values.<\/p>\n<h3>Can you overdose on vitamin C?<\/h3>\n<p>From food alone, no. You would need to eat several kilos of fruit a day to get anywhere near 2 grams. The picture changes with supplements. A single <strong>vitamin C 1,000 mg<\/strong> tablet is on its own nine times the reference intake. Two tablets, an &#8220;immunity&#8221; effervescent and a multivitamin, and you are past the 2,000 mg threshold without noticing. The MSD Manual notes that some people take up to <strong>10 g a day<\/strong> for benefits that have not been demonstrated.<\/p>\n<p>The term <strong>hypervitaminosis C<\/strong> is rarely used, because vitamin C does not build up in the tissues the way vitamins A or D do. <strong>Excess vitamin C<\/strong> shows itself differently: through what the surplus does on its way out, in the gut first, then in the kidneys. So the question is not &#8220;is vitamin C dangerous?&#8221;, but &#8220;at what dose, in what form, and with what kidneys?&#8221;.<\/p>\n<h2>Vitamin C side effects: the symptoms of too much<\/h2>\n<h3>Diarrhoea, nausea, bloating, heartburn: the digestive effects<\/h3>\n<p>This is the best-established side effect. According to the MSD Manual, taking <strong>more than 2 g of vitamin C a day<\/strong> can cause nausea and diarrhoea. The mechanism is simple: beyond a certain amount, the gut no longer absorbs everything, and the vitamin C left in the intestine draws in water. Hence the phrase &#8220;vitamin C laxative effect&#8221; that comes up online. Bloating, cramps, gas and loose stools often set in on the first or second day and disappear when you stop or lower the dose. If the diarrhoea lasts, it can dehydrate you, which is not a good state for your kidneys either. Vitamin C does not cause constipation: if you become constipated on a &#8220;vitamin C + iron&#8221; or &#8220;vitamin C + calcium&#8221; supplement, look at the other ingredient.<\/p>\n<p>Ascorbic acid is, as its name says, an acid. Taken on an empty stomach or as a pure powder, it can cause <strong>heartburn<\/strong>, stomach pain or make reflux worse. Taking it in the middle of a meal, or choosing a buffered form (sodium or calcium ascorbate), solves the problem in most cases. Be careful with sodium ascorbate if you watch your salt intake, which we come back to below.<\/p>\n<h3>Does vitamin C make you sleepy or tired? Sleep, fatigue and headaches<\/h3>\n<p>&#8220;Does ascorbic acid make you sleepy?&#8221; and &#8220;does vitamin C keep you awake?&#8221; are two of the most searched questions, in opposite directions. The honest answer to both: no solid data show that vitamin C affects sleep, either way. Neither the MSD Manual nor EFSA describe such an effect. The impression probably comes from the products it is combined with (caffeine, guarana, &#8220;energy&#8221; complexes) or from a fizzy drink taken late in the evening. If in doubt, take your vitamin C in the morning: it changes nothing about absorption and removes the question.<\/p>\n<p>Likewise, &#8220;too much vitamin C&#8221; does not cause any documented fatigue. Persistent tiredness in someone who supplements should prompt a search for another cause, and often <a href=\"https:\/\/yuboost.com\/en\/expertise\/which-vitamin-deficiency-causes-fatigue\/\">the fatigue has a measurable explanation<\/a>: iron, thyroid, vitamin D, blood sugar. Mild headaches reported with high doses are possible but non-specific.<\/p>\n<h3>Effects on the skin and face<\/h3>\n<p>Taken orally, vitamin C has no skin-related adverse effect described in the MSD Manual. The tingling, redness or irritation you read about under &#8220;vitamin C for the face&#8221; concern cosmetic serums applied to the skin, a dermatology topic separate from supplementation. The same goes for the &#8220;skin whitening&#8221; tablets sold in some countries: no lightening effect is documented, and the digestive and renal thresholds apply exactly as they do to any other tablet. If you want to know what vitamin C really does for the skin and the immune system, our article on <a href=\"https:\/\/yuboost.com\/en\/expertise\/what-are-the-benefits-of-vitamin-c\/\">the benefits of vitamin C<\/a> separates what is proven from what is not.<\/p>\n<h2>Vitamin C, kidney stones and iron: the two real risks of overdose<\/h2>\n<h3>Kidney stones and oxalate<\/h3>\n<p>This is the side effect of vitamin C that justifies medical caution. Part of the ascorbic acid is converted by the body into <strong>oxalate<\/strong>, then cleared by the kidneys. The MSD Manual notes that a high intake causes <strong>hyperoxaluria<\/strong> (excess oxalate in the urine) and thereby promotes the formation of <strong>calcium oxalate kidney stones<\/strong>, the most common type of stone. It adds that the acidification of the urine by vitamin C plays a part.<\/p>\n<p>At very high doses, the problem goes beyond stones. The medical literature describes cases of <strong>oxalate nephropathy<\/strong>: oxalate crystals settle in the kidney tubules and cause acute kidney failure. Two published cases set the orders of magnitude:<\/p>\n<ul>\n<li>A 59-year-old woman whose kidney function had been normal two months earlier took <strong>more than 4 g of vitamin C a day for 30 days<\/strong> as part of an alternative treatment. She developed acute kidney failure with calcium oxalate deposits on biopsy, needed dialysis and did not recover her kidney function (Poulin et al., <em>Clinical Kidney Journal<\/em>, 2014).<\/li>\n<li>Two intensive care patients received <strong>112 g and 160 g of intravenous vitamin C<\/strong> over several days. Both developed oxalate nephropathy. The authors stress that pre-existing kidney damage and the dehydration of critical illness amplified the risk (Fontana et al., <em>Kidney International Reports<\/em>, 2020).<\/li>\n<\/ul>\n<p>These cases are extreme and do not concern the person taking 500 mg in the morning. But they say one thing clearly: <strong>the kidney is the organ that limits vitamin C<\/strong>. A history of kidney stones, kidney failure even when mild, dehydration, bariatric surgery or a digestive disease that increases oxalate absorption: in these situations, high doses of vitamin C are to be avoided, and any high-dose infusion must be preceded by a measurement of kidney function. YuBoost&#8217;s <a href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/\">complete medical check-up<\/a> includes kidney function (creatinine, urea, filtration rate) among its 34 biomarkers, at home and with no prescription needed.<\/p>\n<h3>Vitamin C and iron: caution in iron overload<\/h3>\n<p>Vitamin C increases the intestinal absorption of non-haem iron, the iron found in plants. That is a useful property when you are short of iron: a glass of orange juice with your lentils improves uptake. It is a risk in the opposite situation. The MSD Manual states that in people with <strong>thalassaemia<\/strong> or <strong>haemochromatosis<\/strong>, a high vitamin C intake can worsen <strong>iron overload<\/strong>. Hereditary haemochromatosis often goes unnoticed for years and is picked up on a high ferritin found by chance.<\/p>\n<p>In other words, taking high-dose vitamin C for years without knowing your iron status is not trivial. <strong>Ferritin<\/strong>, transferrin and serum iron are among the 11 biomarkers of the <a href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/\">vitamin and mineral check-up<\/a>. An unexplained high ferritin deserves a medical opinion before any supplementation, with vitamin C as much as with iron.<\/p>\n<h2>Side effects by form: tablets, effervescents, liposomal, zinc + vitamin C<\/h2>\n<h3>500 mg and 1,000 mg tablets and capsules<\/h3>\n<p>The most common form. One tablet a day stays below the 2,000 mg threshold. The <strong>side effects of vitamin C 1,000 mg tablets<\/strong> appear mostly when several products are combined, or in people with a sensitive digestion. The rule: add up every source (tablet, multivitamin, effervescent, fortified drink) before judging the dose. Taking vitamin C tablets daily for months is not a problem in itself for a healthy adult; it becomes one when the total creeps above 2 g, or when the kidneys or iron stores are not what you assume.<\/p>\n<h3>Effervescent tablets: the sodium you cannot see<\/h3>\n<p>Effervescent tablets contain sodium bicarbonate or carbonate to make the bubbles. That dose of salt goes unnoticed, since nothing tastes salty. A case-control study published in the <em>BMJ<\/em> in 2013, covering more than 1.29 million patients in the United Kingdom, compared people taking effervescent, dispersible or soluble medicines containing sodium with people taking the same active ingredients in standard formulations. The result: a <strong>16%<\/strong> higher risk of a cardiovascular event (heart attack, stroke, vascular death), with an odds ratio of 1.16, and a risk of <strong>hypertension<\/strong> multiplied by 7 (odds ratio 7.18). The authors recommend prescribing sodium-containing forms with caution, and only when the expected benefit outweighs this risk.<\/p>\n<p>That study looked at medicines, not specifically at vitamin C, but the sodium is the same. If you have high blood pressure, heart failure or kidney failure, or if your doctor has asked you to cut down on salt, a daily effervescent is not the right form. A standard tablet delivers the same vitamin C without the sodium.<\/p>\n<h3>Liposomal vitamin C<\/h3>\n<p>Liposomal vitamin C is ascorbic acid wrapped in phospholipids, sold on the promise of better absorption. On adverse effects, there are no specific data: the active molecule is the same, the digestive and renal thresholds apply in the same way, and if absorption really is better, so is the amount that reaches the kidneys. There is therefore no reason to regard the liposomal form as &#8220;free of side effects&#8221;. The doses sold (often 1,000 mg per serving) count towards the daily total like any other.<\/p>\n<h3>Zinc + vitamin C, vitamin C + calcium, acerola, powders<\/h3>\n<p>The digestive effects reported with the &#8220;zinc + vitamin C&#8221; supplements sold for immunity can come from either of the two ingredients. Before blaming the vitamin C, read the zinc dose on the label. The same applies to &#8220;vitamin C + calcium&#8221; products, where calcium is the more likely cause of constipation or bloating. For the combinations worth watching, see <a href=\"https:\/\/yuboost.com\/en\/expertise\/which-vitamins-cant-be-taken-together\/\">which vitamins can&#8217;t be taken together<\/a>. Pure ascorbic acid powders, often measured out by the spoon, are the easiest form to overdose on: one level teaspoon is already several grams.<\/p>\n<h2>High-dose intravenous vitamin C: side effects and contraindications<\/h2>\n<p>Taken orally, the gut caps what gets into the blood. With a <strong>vitamin infusion<\/strong>, that cap disappears: the whole dose enters the circulation, and the blood concentrations reached are on another scale from those of a tablet. At YuBoost, the <a href=\"https:\/\/yuboost.com\/en\/iv-therapy\/high-dose-vitamin-c\/\">High Dose Vitamin C<\/a> infusion delivers 7.5 g of vitamin C in about an hour, at home. It is offered <strong>on medical indication only<\/strong>, after an online consultation with a doctor and an individual assessment. Three points of vigilance explain that rule.<\/p>\n<h3>G6PD deficiency: the risk of haemolysis<\/h3>\n<p>Glucose-6-phosphate dehydrogenase (G6PD) deficiency is, according to the MSD Manual, the most common disorder of red blood cell metabolism. It affects more than 10% of men of African descent and is common in populations from the Mediterranean basin (Italy, Greece, the Middle East) and from Asia. Most people who have it do not know: they are fine until the day an oxidising substance triggers a sudden destruction of red blood cells, <strong>haemolysis<\/strong>, with jaundice, dark urine, back pain and sometimes kidney injury.<\/p>\n<p>At very high doses, vitamin C behaves as an oxidant. A review published in 2022 in the <em>Indian Journal of Critical Care Medicine<\/em> gathered the <strong>14 published cases of haemolysis attributed to vitamin C<\/strong> between 1975 and 2020. Ten of them, <strong>71.4%<\/strong>, had G6PD deficiency. Doses ranged from 1 to 200 g a day, the intravenous route was involved in 57% of cases, and 11 of the 14 patients developed complications within <strong>3 days<\/strong> of starting treatment. Nearly half had acute kidney injury.<\/p>\n<p>The threshold is debated. In <em>Critical Care<\/em> in 2019, Paul Marik points out that the haemolysis cases involve very high pharmacological doses, above 60 g, and argues that 6 g a day should not be regarded as contraindicated in G6PD deficiency. Most clinical trials nonetheless exclude these patients as a precaution. Our position is simple: at 7.5 g per infusion, we do not take the risk blind. If you are of African, Mediterranean or Asian descent, or if you have ever had an unexplained episode of jaundice, a G6PD test is requested before any high-dose infusion.<\/p>\n<h3>Kidney function and hydration<\/h3>\n<p>The oxalate nephropathy cases described above all involved high or repeated intravenous doses, often in patients whose kidneys were already weakened. <strong>Kidney failure<\/strong>, even when mild, and a history of <strong>kidney stones<\/strong> are contraindications to high-dose vitamin C. That is why kidney function is measured before the infusion, and why you are asked to drink well before and after.<\/p>\n<h3>Diabetes: distorted glucose meter readings<\/h3>\n<p>A less well-known effect, but a documented one. After a high-dose vitamin C infusion, the blood concentration of ascorbic acid is high enough to interfere with strip-based glucose meters. A case published in 2013 in the <em>Journal of Diabetes Investigation<\/em> describes a diabetic patient who received 50 g of intravenous vitamin C: one meter showed severe hypoglycaemia, another major hyperglycaemia, while the laboratory assay gave a normal reading of 9.2 mmol\/L. The danger is injecting insulin, or glucose, on the basis of a false value. If you have insulin-treated diabetes, say so before any infusion: blood sugar is then checked in the laboratory, not on the meter, in the hours that follow.<\/p>\n<h3>Mild effects possible during the infusion<\/h3>\n<p>The effects commonly reported with high-dose vitamin infusions remain modest: a feeling of warmth or thirst, discomfort at the needle site, passing nausea, needing to urinate more often in the following hours. They are monitored by the nurse on site. To find out what this route of administration can realistically deliver, read our analysis of <a href=\"https:\/\/yuboost.com\/en\/expertise\/the-effectiveness-of-intravenous-vitamin-infusions\/\">the effectiveness of intravenous vitamin infusions<\/a>.<\/p>\n<div class=\"yb-art-quote\">\n<p>The question I ask before any high-dose vitamin C infusion is not &#8220;do you want to boost your immunity?&#8221; but &#8220;how are your kidneys, and do you know your G6PD status?&#8221;. An infusion is prescribed on a blood test, never on a whim.<\/p>\n<p>          <cite>Dr Alexandra Miles, YuBoost<\/cite>\n        <\/div>\n<h2>Vitamin C and blood pressure, pregnancy, diabetes: the recurring questions<\/h2>\n<p><strong>Vitamin C and high blood pressure.<\/strong> Vitamin C does not raise blood pressure. A meta-analysis published in 2012 in the <em>American Journal of Clinical Nutrition<\/em>, pooling 29 randomised trials and 1,407 participants with a median dose of 500 mg a day, measured a modest fall in blood pressure: <strong>3.84 mmHg<\/strong> systolic and 1.48 mmHg diastolic, in short trials (8 weeks on median). The authors call for longer trials before drawing any recommendation. The only link between vitamin C and hypertension that should concern you is the sodium in effervescents, described above.<\/p>\n<p><strong>Vitamin C and pregnancy.<\/strong> Needs rise slightly (120 mg a day according to ANSES, 170 mg while breastfeeding) and are covered by a varied diet. EFSA has set no specific upper limit for pregnancy, for lack of data, which is a reason to stay within usual doses. High doses and infusions are not justified without medical advice during this period.<\/p>\n<p><strong>Vitamin C and diabetes.<\/strong> At usual oral doses, no demonstrated effect on blood sugar. The point of vigilance is the one described above: at very high doses, vitamin C distorts glucose meter readings, in one direction or the other depending on the device&#8217;s technology.<\/p>\n<p><strong>Men and women.<\/strong> The side effects of vitamin C are the same in both sexes. The only difference in the references is the reference intake (75 mg for women versus 90 mg for men in the US values), which does not change the 2,000 mg threshold.<\/p>\n<h2>Vitamin C contraindications: who should avoid it or ask a doctor<\/h2>\n<p>The <strong>contraindications of vitamin C<\/strong> come down to a few situations, mostly involving high doses and the intravenous route:<\/p>\n<ul>\n<li><strong>History of kidney stones or kidney failure<\/strong>: avoid doses above the reference intake and any high-dose infusion without a prior measurement of kidney function (MSD Manual, published cases of oxalate nephropathy).<\/li>\n<li><strong>Haemochromatosis, thalassaemia, high ferritin<\/strong>: vitamin C worsens iron overload (MSD Manual). Have your ferritin measured before supplementing.<\/li>\n<li><strong>G6PD deficiency<\/strong>, known or suspected: contraindication to high-dose intravenous vitamin C, because of the risk of haemolysis. Usual oral doses are not concerned.<\/li>\n<li><strong>High blood pressure, heart failure, low-salt diet<\/strong>: avoid effervescent forms and sodium ascorbate, prefer a standard tablet.<\/li>\n<li><strong>Insulin-treated diabetes<\/strong>: no contraindication to vitamin C itself, but a laboratory blood sugar check after any high-dose infusion.<\/li>\n<li><strong>Long-term treatment<\/strong> (anticoagulant, chemotherapy, iron chelation): tell your doctor or pharmacist about any supplement, even a &#8220;natural&#8221; one.<\/li>\n<\/ul>\n<p>For the other vitamins, some of which build up in the body and raise different problems, see <a href=\"https:\/\/yuboost.com\/en\/expertise\/what-are-the-risks-of-taking-too-many-vitamins\/\">what are the risks of taking too many vitamins<\/a> and, for the B group, <a href=\"https:\/\/yuboost.com\/en\/expertise\/what-are-the-side-effects-of-vitamin-b\/\">the side effects of vitamin B<\/a>.<\/p>\n<h2>Too much vitamin C: the overdose symptoms that should alert you<\/h2>\n<p>If you take a vitamin C supplement and recognise yourself in any of these signs, do not increase the dose, and see a doctor:<\/p>\n<ul>\n<li>Diarrhoea, nausea or abdominal cramps that last more than a few days;<\/li>\n<li>Sudden pain in the lower back or flank, radiating towards the groin, blood in the urine (signs of a kidney stone);<\/li>\n<li>Passing less urine, swollen legs, unusual tiredness after a high dose or an infusion (renal signs);<\/li>\n<li>Jaundice, very dark urine, breathlessness, back pain in the days after a high-dose infusion (signs of haemolysis, emergency);<\/li>\n<li>Blood pressure that has been climbing since you switched to a daily effervescent;<\/li>\n<li>Swelling of the face or lips, hives, difficulty breathing (allergic reaction, rare but possible with any supplement, emergency).<\/li>\n<\/ul>\n<p>Conversely, slightly yellower urine or needing to urinate more often after a high dose are not signs of overdose. That is the surplus leaving the body.<\/p>\n<h2>Should you have a blood test before taking vitamin C?<\/h2>\n<p>Not for the occasional tablet during a cold. Yes, as soon as the intake becomes daily and prolonged, the dose exceeds 1,000 mg, or a high-dose infusion is being considered. The logic is the same as for any supplement: you only correct what is missing, and you check that the body can handle what you give it. A genuine <strong>vitamin C deficiency<\/strong> shows up in a blood test (a level below 0.2 mg\/dL according to the MSD Manual) and is treated with 500 to 1,000 mg a day for one to two weeks, not with grams for years. To recognise the signs of a shortfall, <a href=\"https:\/\/yuboost.com\/en\/expertise\/how-can-you-tell-if-you-have-a-vitamin-deficiency\/\">how can you tell if you have a vitamin deficiency<\/a> gives you the pointers; to know when supplementing makes sense, read <a href=\"https:\/\/yuboost.com\/en\/expertise\/in-what-cases-should-vitamin-c-be-taken\/\">in what cases vitamin C should be taken<\/a>.<\/p>\n<p>YuBoost&#8217;s <a href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/\">complete medical check-up<\/a> measures <strong>34 biomarkers<\/strong>, including <strong>kidney function<\/strong>, blood count, blood sugar, liver, thyroid and inflammation: exactly what determines whether a vitamin C supplement or infusion is safe for you. How it works:<\/p>\n<ul>\n<li><strong>Blood draw at home<\/strong> by a registered nurse, <strong>no prescription needed<\/strong>, in Lausanne, Geneva, Zurich and across French-speaking Switzerland;<\/li>\n<li><strong>Analysis in an accredited Swiss laboratory<\/strong>, results within 7 working days;<\/li>\n<li><strong>Personalised medical report<\/strong> and an optional online consultation with a doctor.<\/li>\n<\/ul>\n<p>The check-up costs <strong>CHF 350<\/strong>. If your question is about iron, the <a href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/\">vitamin and mineral check-up<\/a> (CHF 370) measures ferritin, transferrin and iron along with eight other markers. When a deficiency is confirmed or a medical indication is established, a <a href=\"https:\/\/yuboost.com\/en\/expertise\/what-exactly-are-vitamin-c-injections\/\">vitamin C injection<\/a> or the <a href=\"https:\/\/yuboost.com\/en\/iv-therapy\/high-dose-vitamin-c\/\">High Dose Vitamin C<\/a> infusion (7.5 g, CHF 450) can be offered, at home, after assessment by a doctor. For the full picture of the vitamin itself, roles, needs, food sources and routes of administration, see our <a href=\"https:\/\/yuboost.com\/en\/vitamins\/vitamin-c\/\">vitamin C guide<\/a>. Vitamin C side effects are not inevitable: they are a matter of dose, form and individual terrain, and the only way to avoid them is to know yours before you start.<\/p>\n<h2>Frequently asked questions<\/h2>\n<div class=\"yb-art-faq\">\n<details open>\n<summary>What are the side effects of vitamin C?<\/summary>\n<p>At dietary doses, none. With supplements, the effects documented by the MSD Manual are nausea and diarrhoea above 2,000 mg a day, and an increase in urinary oxalate that promotes kidney stones. In people with haemochromatosis or thalassaemia, vitamin C worsens iron overload. Effervescent forms add sodium, a problem in case of high blood pressure.<\/p>\n<\/details>\n<details>\n<summary>What happens if you take too much vitamin C?<\/summary>\n<p>Most of the surplus is passed out in the urine, which explains the absence of acute toxicity at usual doses. Above 2 g a day, the gut can no longer keep up and diarrhoea appears. Over time, or at very high doses, the kidney takes the hit: calcium oxalate stones and, in published cases from 4 g a day for a month, acute kidney failure.<\/p>\n<\/details>\n<details>\n<summary>Do vitamin C 1,000 mg tablets have side effects?<\/summary>\n<p>One 1,000 mg tablet a day stays below the 2,000 mg upper limit set by the US authorities and cited by the MSD Manual. Digestive effects appear mostly when several products are combined or in sensitive people. If you have a history of kidney stones or a high ferritin, even 1,000 mg a day over the long term deserves a medical opinion.<\/p>\n<\/details>\n<details>\n<summary>Does vitamin C cause kidney stones?<\/summary>\n<p>It increases the risk at high doses. Part of the vitamin C is converted into oxalate, and the MSD Manual states that a high intake promotes calcium oxalate stones. The risk is greater in people who have already had stones, in kidney failure or in dehydration. These people should stick to the reference intake.<\/p>\n<\/details>\n<details>\n<summary>Does ascorbic acid make you sleepy, or keep you awake?<\/summary>\n<p>Neither is supported by scientific data, and neither the MSD Manual nor EFSA describe an effect on sleep or alertness. The impression often comes from the products it is combined with (caffeine, &#8220;energy&#8221; complexes). If in doubt, take vitamin C in the morning: its absorption does not depend on the time of day.<\/p>\n<\/details>\n<details>\n<summary>Do effervescent vitamin C tablets have specific side effects?<\/summary>\n<p>Yes, because of the sodium they contain to produce the bubbles. A 2013 <em>BMJ<\/em> study of 1.29 million patients linked sodium-containing effervescent and soluble medicines to a 16% higher cardiovascular risk and a sevenfold higher risk of hypertension compared with the same active ingredients in standard tablets. If you have high blood pressure or follow a low-salt diet, choose a non-effervescent tablet.<\/p>\n<\/details>\n<details>\n<summary>What are the side effects of intravenous vitamin C?<\/summary>\n<p>Mild effects (warmth, thirst, discomfort at the needle site, passing nausea) are common and harmless. The serious risks concern specific profiles: haemolysis in G6PD deficiency (10 of the 14 published cases), oxalate nephropathy in kidney failure, and distorted glucose meter readings in diabetics. That is why a high-dose infusion is given on medical indication only, after a blood test.<\/p>\n<\/details>\n<details>\n<summary>How do I know whether I can take vitamin C safely?<\/summary>\n<p>By checking three things: your kidney function, your ferritin and, before a high-dose infusion, your G6PD status. YuBoost&#8217;s complete medical check-up measures kidney function, blood sugar and blood count among 34 biomarkers, at home and with no prescription needed in Lausanne, Geneva, Zurich and across French-speaking Switzerland, with results interpreted by a doctor.<\/p>\n<\/details><\/div>\n<h2>Sources<\/h2>\n<p class=\"yb-art-sources\">\n          \u2022 MSD Manual Professional Edition, <em>Vitamin C Toxicity<\/em> (2,000 mg\/day upper limit, nausea and diarrhoea, hyperoxaluria and stones, iron overload): <a href=\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/vitamin-c-toxicity\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 MSD Manual Professional Edition, <em>Vitamin C Deficiency<\/em> (recommended intakes, smokers, deficiency threshold, treatment): <a href=\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/vitamin-c-deficiency\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 MSD Manual Professional Edition, <em>Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency<\/em> (prevalence, populations, triggers, symptoms): <a href=\"https:\/\/www.msdmanuals.com\/professional\/hematology-and-oncology\/anemias-caused-by-hemolysis\/glucose-6-phosphate-dehydrogenase-g6pd-deficiency\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 EFSA, <em>Summary of Tolerable Upper Intake Levels<\/em>, 2024 version (vitamin C: no adequate data to derive a UL): <a href=\"https:\/\/www.efsa.europa.eu\/sites\/default\/files\/2024-05\/ul-summary-report.pdf\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 ANSES, <em>Dietary reference values for vitamins and minerals<\/em> (vitamin C: 110 mg\/day adults, 120 mg pregnancy, 170 mg breastfeeding): <a href=\"https:\/\/www.anses.fr\/en\/content\/dietary-reference-values-vitamins-and-minerals\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Poulin L.-D. et al., <em>Acute oxalate nephropathy induced by oral high-dose vitamin C alternative treatment<\/em>, Clinical Kidney Journal, 2014: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC3970339\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Fontana F. et al., <em>Oxalate Nephropathy Caused by Excessive Vitamin C Administration in 2 Patients With COVID-19<\/em>, Kidney International Reports, 2020: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC7363608\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Juneja D., Jain R., Nasa P., <em>Vitamin C-induced Hemolysis: Meta-summary and Review of Literature<\/em>, Indian Journal of Critical Care Medicine, 2022: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC8857720\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Marik P. E., <em>Is intravenous vitamin C contraindicated in patients with G6PD deficiency?<\/em>, Critical Care, 2019: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC6448313\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Kimura T. et al., <em>Pseudohypoglycemia or hyperglycemia caused by interference with self-monitoring blood glucose measurements in anticancer ascorbic acid therapy<\/em>, Journal of Diabetes Investigation, 2013: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC4020267\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 George J. et al., <em>Association between cardiovascular events and sodium-containing effervescent, dispersible, and soluble drugs: nested case-control study<\/em>, BMJ, 2013: <a href=\"https:\/\/discovery.dundee.ac.uk\/en\/publications\/association-between-cardiovascular-events-and-sodium-containing-e\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Juraschek S. P. et al., <em>Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials<\/em>, American Journal of Clinical Nutrition, 2012: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC3325833\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Swiss Society for Nutrition SSN, <em>Referenzwerte f\u00fcr die N\u00e4hrstoffzufuhr<\/em> (reference values, in German): <a href=\"https:\/\/www.sge-ssn.ch\/de\/empfehlungen\/naehrstoffe-lebensmittel\/referenzwerte\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a>\n        <\/p>\n<\/p><\/div>\n<aside class=\"yb-art-aside\">\n<div class=\"yb-art-panel yb-art-panel--cta\">\n<div class=\"k\">Take action<\/div>\n<h3>Check your <em>kidneys<\/em> before high-dose vitamin C<\/h3>\n<p>Kidney function, blood sugar, blood count, liver, thyroid: 34 biomarkers. At home, no prescription needed, across French-speaking Switzerland.<\/p>\n<p>          <a class=\"yb-art-sbtn yb-art-sbtn--p\" href=\"https:\/\/yuboost.com\/en\/booking\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=cta-side\">Book an appointment<\/a><br \/>\n          <a class=\"yb-art-sbtn yb-art-sbtn--g\" href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=cta-side-checkup\">See the check-up: CHF 350<\/a>\n        <\/div>\n<p>        <a class=\"yb-art-panel yb-art-panel--author\" href=\"https:\/\/yuboost.com\/en\/about-us\/\"><br \/>\n          <img decoding=\"async\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\" alt=\"Dr Alexandra Miles\"><\/p>\n<div><strong>Dr Alexandra Miles<\/strong><span>CEO YuBoost \u00b7 Functional medicine<\/span><\/div>\n<p>        <\/a><br \/>\n      <\/aside>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"yb-rel\">\n<div class=\"yb-rel__head\">\n      <span class=\"yb-art-eyebrow\">Go further<\/span><\/p>\n<h2>Measure before you supplement<\/h2>\n<p>At home across French-speaking Switzerland, no prescription needed.<\/p>\n<\/p><\/div>\n<div class=\"yb-rel__viewport\">\n      <button type=\"button\" class=\"yb-rel__nav yb-rel__nav--prev\" aria-label=\"Previous\"><svg viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" aria-hidden=\"true\"><path d=\"M15 18l-6-6 6-6\"\/><\/svg><\/button><\/p>\n<div class=\"yb-rel__track-wrap\">\n<div class=\"yb-rel__track\">\n<p>          <a class=\"yb-rel__card yb-rel__card--featured\" href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=rel-checkup\"><br \/>\n            <span class=\"yb-rel__badge yb-rel__badge--top\">Most relevant<\/span><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/04\/bilan-sanguin-complet.png\" alt=\"Complete medical check-up with kidney function, at home in Switzerland, before vitamin C supplementation\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Complete check-up<\/p>\n<h3 class=\"yb-rel__name\">Complete medical check-up<\/h3>\n<p class=\"yb-rel__desc\">34 biomarkers: kidney function, blood sugar, blood count, liver, thyroid, inflammation. At home.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">Kidney function<\/span><span class=\"yb-rel__chip\">34 markers<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">CHF 350<\/span><span class=\"yb-rel__cta\">Book<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p>\n<p>          <a class=\"yb-rel__card\" href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=rel-vitamins\"><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/06\/Bilan-vitamines.png\" alt=\"Vitamin and mineral check-up with ferritin and iron testing at home in Switzerland\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Deficiencies &amp; iron<\/p>\n<h3 class=\"yb-rel__name\">Vitamin &amp; mineral check-up<\/h3>\n<p class=\"yb-rel__desc\">Iron, ferritin, transferrin, vitamins B6, B9, B12 and D, magnesium, calcium, zinc. At home.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">Ferritin<\/span><span class=\"yb-rel__chip\">11 markers<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">CHF 370<\/span><span class=\"yb-rel__cta\">Book<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p>\n<p>          <a class=\"yb-rel__card\" href=\"https:\/\/yuboost.com\/en\/iv-therapy\/high-dose-vitamin-c\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=rel-highdose\"><br \/>\n            <span class=\"yb-rel__badge yb-rel__badge--new\">On medical indication<\/span><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/03\/HighDoseVitaminC.png\" alt=\"High-dose vitamin C infusion at home in Switzerland, on medical indication\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Vitamin infusion<\/p>\n<h3 class=\"yb-rel__name\">High Dose Vitamin C<\/h3>\n<p class=\"yb-rel__desc\">Vitamin C 7.5 g. After a blood test and medical consultation, at home, about 60 minutes.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">7.5 g<\/span><span class=\"yb-rel__chip\">60 min<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">CHF 450<\/span><span class=\"yb-rel__cta\">Discover<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p>\n<p>          <a class=\"yb-rel__card\" href=\"https:\/\/yuboost.com\/en\/vitamins\/vitamin-c\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=rel-vitamin-c\"><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/04\/EN-Vitamin-C-e1776841839202.png\" alt=\"Vitamin C guide: roles, needs, deficiency and routes of administration, YuBoost Switzerland\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Vitamin C<\/p>\n<h3 class=\"yb-rel__name\">Vitamin C guide<\/h3>\n<p class=\"yb-rel__desc\">The complete guide: roles, needs, deficiency, food sources and routes of administration.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">Guide<\/span><span class=\"yb-rel__chip\">At home<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">Discover<\/span><span class=\"yb-rel__cta\">View<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p><\/div>\n<\/p><\/div>\n<p>      <button type=\"button\" class=\"yb-rel__nav yb-rel__nav--next\" aria-label=\"Next\"><svg viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" aria-hidden=\"true\"><path d=\"M9 18l6-6-6-6\"\/><\/svg><\/button>\n    <\/div>\n<div class=\"yb-rel__dots\"><\/div>\n<\/p><\/div>\n<div class=\"yb-art-container\">\n<div class=\"yb-art-cta\">\n<div class=\"yb-art-cta-blob\"><\/div>\n<div class=\"yb-art-cta-in\">\n        <span class=\"yb-art-eyebrow\">Take action<\/span><\/p>\n<h2>Measure before you <span class=\"yb-art-accent\">supplement<\/span><\/h2>\n<p class=\"yb-art-cta-sub\">Kidney function, blood sugar, blood count, liver and thyroid in a single check-up, at home across French-speaking Switzerland and with no prescription needed. Blood draw by a registered nurse, results interpreted by a doctor. The high-dose vitamin C infusion comes only after.<\/p>\n<p>        <a class=\"yb-art-btn\" href=\"https:\/\/yuboost.com\/en\/booking\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=cta-final\">Book an appointment<\/a><br \/>\n        <a class=\"yb-art-btn-ghost\" href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-c-side-effects&#038;utm_content=cta-final-checkup\">See the check-up: CHF 350<\/a>\n      <\/div>\n<\/p><\/div>\n<p class=\"yb-art-disc\">This article is for information only and does not replace individual medical advice. In case of sudden lower back pain, blood in the urine, jaundice or an allergic reaction after taking vitamin C, consult a healthcare professional. Reviewed by Dr Alexandra Miles, September 2026.<\/p>\n<\/p><\/div>\n<\/div>\n<\/div>\n<p><!--more--><br \/>\n<!-- {\"type\":\"layout\",\"children\":[{\"type\":\"section\",\"props\":{\"image_position\":\"center-center\",\"status\":\"disabled\",\"style\":\"default\",\"title_breakpoint\":\"xl\",\"title_position\":\"top-left\",\"title_rotation\":\"left\",\"vertical_align\":\"\",\"width\":\"large\"},\"children\":[{\"type\":\"row\",\"props\":{\"layout\":\"3-4,1-4\",\"row_gap\":\"large\"},\"children\":[{\"type\":\"column\",\"props\":{\"image_position\":\"center-center\",\"position_sticky_breakpoint\":\"m\",\"width_medium\":\"3-4\"},\"children\":[{\"type\":\"headline\",\"props\":{\"css\":\".el-element {\\n    text-transform : uppercase;}\",\"image_align\":\"left\",\"image_margin\":\"xsmall\",\"title_element\":\"h1\",\"title_style\":\"heading-small\",\"yooessentials_access_conditions\":[],\"yooessentials_access_mode\":\"AND\"},\"source\":{\"props\":{\"content\":{\"filters\":{\"search\":\"\"},\"name\":\"title\"}},\"query\":{\"name\":\"pages.singlePage\"}}},{\"type\":\"breadcrumbs\",\"props\":{\"show_current\":true,\"show_home\":true}},{\"type\":\"text\",\"props\":{\"column_breakpoint\":\"m\",\"content\":\"\n\n<p>Vitamin C or ascorbic acid, a water-soluble vitamin, is found in citrus fruit, such as oranges, lemons and grapefruit, as well as in many other fruit and vegetables. The average recommended daily intake of vitamin C for women is 75 milligrams and 90 milligrams for men. This vitamin boasts great benefits for the body: skin healthiness, anti-aging effect, boosts immunity defences, is an energy booster and helps prevent some diseases and infections. Vitamin C deficiency can occur as a result of a poor diet, smoking, excess drugs and alcohol, and due to specific risk factors (aging, sun exposure, genetics) and pathologies (immunodeficient people, diabetics, people suffering from inflammatory disorders). Here, at YuBoost, we propose several IV therapies to enable your body to assimilate vitamins, minerals and antioxidants rapidly and effectively. However, you must always be aware that overdoses are possible. Side effects are likely to occur when you have excess vitamin C in your body, as the body can't stock the excess. There are also contraindications to ascorbic acid supplements if you have a certain medical history or take specific medication.<\/p>\n\n\",\"margin_bottom\":\"default\",\"margin_top\":\"default\",\"text_align\":\"justify\"}},{\"type\":\"image\",\"props\":{\"image\":\"wp-content\/uploads\/2023\/06\/3-1.png\",\"image_alt\":\"vitamine carence\",\"image_loading\":true,\"image_svg_color\":\"emphasis\",\"margin_bottom\":\"default\",\"margin_top\":\"default\"}},{\"type\":\"text\",\"props\":{\"column_breakpoint\":\"m\",\"content\":\"\n\n<h2>Vitamin C deficiency risks<\/h2>\n\n\\n\n\n<p>Vitamin C deficiency can lead to a number of different symptoms: severe fatigue, mood disorders, joint pain, anaemia, weight loss, etc. Various dermatological symptoms can also occur: dry skin, blotchy skin, hair loss, brittle nails, bleeding around the gums and poor wound healing.\u00a0 A vitamin C supplement can as such bean option to remedy this deficiency. Intravenous vitamin injections are the perfect solution for relieving your symptoms rapidly: the vitamin is directly assimilated in your bloodstream without travelling through the digestive wall and ,as such, you can feel its benefits a few hours after the infusion.<\/p>\n\n\\n\n\n<h2>Excess vitamin C side effects: digestive and urinary disorders, insomnia<\/h2>\n\n\\n\n\n<p>High intakes of vitamin C may, in some cases, cause gastrointestinal disorders, such as rapid transit, nausea, bloating, abdominal pain and heartburn. These symptoms may be accompanied by slight headaches. If diarrhoea occurs, it's vital to drink enough water to prevent any risk of dehydration. Urinary disorders may also occur: some patients may feel discomfort when passing urine or may notice abnormal urine colour. In addition, some people state they have problems falling asleep after having taken vitamin C. Ascorbic acid supplements should be taken preferably at the beginning of the day and should be avoided in the evening so as not to interfere with sleep quality.<\/p>\n\n\\n\n\n<h2>Vitamin C supplement contraindications<\/h2>\n\n\\n\n\n<p>A vitamin C supplement is not recommended for people with a history of kidney stones or severe renal insufficiency. This is because part of the ascorbic acid eliminated in the urine is in the form of oxalate, a chemical compound responsible for the majority of kidney stones. A vitamin C supplement should also be avoided in people who have excess iron in their blood. As ascorbic acid promotes the intestinal absorption of iron, this could worsen iron overload. Those who take specific medication (deferoxamine, simvastatin, warfarin) should also be vigilant as ascorbic acid can interfere with these treatments<\/p>\n\n\",\"margin_bottom\":\"default\",\"margin_top\":\"default\",\"text_align\":\"justify\"}},{\"type\":\"pagination\",\"props\":{\"margin_bottom\":\"remove\",\"margin_top\":\"large\",\"pagination_space_between\":true,\"pagination_type\":\"previous\/next\",\"text_align\":\"center\"}}]},{\"type\":\"column\",\"props\":{\"image_position\":\"center-center\",\"position_sticky\":\"section\",\"position_sticky_breakpoint\":\"m\",\"width_medium\":\"1-4\"},\"children\":[{\"type\":\"text\",\"props\":{\"column_breakpoint\":\"m\",\"content\":\"Hair Stylist and Owner\",\"margin_bottom\":\"small\",\"margin_top\":\"small\",\"text_align\":\"left\",\"text_align_breakpoint\":\"m\",\"text_align_fallback\":\"center\",\"text_style\":\"meta\"}},{\"type\":\"headline\",\"props\":{\"content\":\"ARTICLES 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datetime=\\\"2017-11-26T17:53:30+00:00\\\">26 November 2017<\/time>\"},\"source\":{\"query\":{\"name\":\"posts.customPosts\",\"arguments\":{\"terms\":[1,10,23],\"category_operator\":\"IN\",\"post_tag_operator\":\"IN\",\"users\":[],\"users_operator\":\"IN\",\"offset\":0,\"limit\":10,\"order\":\"date\",\"order_direction\":\"DESC\"}},\"props\":{\"title\":{\"filters\":{\"search\":\"\"},\"name\":\"title\"},\"image\":{\"filters\":{\"search\":\"\"},\"name\":\"featuredImage.url\"},\"link\":{\"filters\":{\"search\":\"\"},\"name\":\"link\"}}}}]}]}]}],\"name\":\"Post\"},{\"type\":\"section\",\"props\":{\"image_position\":\"center-center\",\"style\":\"default\",\"title_breakpoint\":\"xl\",\"title_position\":\"top-left\",\"title_rotation\":\"left\",\"vertical_align\":\"middle\",\"width\":\"default\"},\"children\":[{\"type\":\"row\",\"children\":[{\"type\":\"column\",\"props\":{\"image_position\":\"center-center\",\"position_sticky_breakpoint\":\"m\"},\"children\":[{\"type\":\"html\",\"props\":{\"content\":\"\n\n<style>\\n  \/* Sans effet visible sur desktop *\/\\n  .yb-art-layout > *{min-width:0;}\\n  .yb-art-body{min-width:0;}\\n  .yb-art-body img{max-width:100%;height:auto;}\\n  .yb-art-tablewrap{max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch;}\\n\\n  @media (max-width:900px){\\n    .yb-art, .yb-art *{box-sizing:border-box;}\\n    .yb-art{max-width:100%;overflow-x:hidden;}\\n    .yb-art-body{max-width:100%;overflow-wrap:break-word;}\\n    .yb-art-table{min-width:560px;}\\n    .yb-art-layout{display:block !important;grid-template-columns:minmax(0,1fr) !important;}\\n    .yb-art-aside{position:static !important;width:100% !important;margin-top:32px;}\\n  }\\n\\n  @media (max-width:600px){\\n    .yb-art-container{padding-left:18px !important;padding-right:18px !important;width:100% !important;max-width:100% !important;}\\n    .yb-art-hero,\\n    .yb-art-key,\\n    .yb-art-quote,\\n    .yb-art-cta{max-width:100% !important;width:100% !important;margin-left:0 !important;margin-right:0 !important;}\\n    .yb-art-hero-in,\\n    .yb-art-cta-in{padding-left:20px !important;padding-right:20px !important;}\\n    .yb-art-hero h1{font-size:clamp(26px,7vw,34px);line-height:1.2;}\\n    .yb-art-meta{flex-wrap:wrap;gap:6px;}\\n    .yb-art-cta-btns{flex-direction:column;align-items:stretch;}\\n    .yb-art-cta-btns > a{text-align:center;}\\n  }\\n<\/style>\n\n\\n\n\n<div class=\\\"yb-art\\\">\\n\\n  \n\n<div class=\\\"yb-art-container\\\">\\n\\n    \n\n<nav class=\\\"yb-art-crumb\\\"><a href=\\\"\/en\/\\\">Home<\/a> \u203a <a href=\\\"\/en\/our-articles\/\\\">Our articles<\/a> \u203a <span>Vitamin C side effects<\/span><\/nav>\n\n\\n\\n    \n\n<div class=\\\"yb-art-hero\\\">\\n      \n\n<div class=\\\"yb-art-hero-blob\\\"><\/div>\n\n\\n      \n\n<div class=\\\"yb-art-hero-in\\\">\\n        <span class=\\\"yb-art-eyebrow\\\">Vitamins &amp; safety<\/span>\\n        \n\n<h1>Vitamin C <span class=\\\"yb-art-accent\\\">side effects<\/span>, overdose and contraindications<\/h1>\n\n\\n        \n\n<p class=\\\"yb-art-hero-sub\\\">1,000 mg tablets, effervescents, liposomal vitamin C, high-dose infusions: which side effects of vitamin C are real, from what dose, and who should avoid it. A review based on the MSD Manual, EFSA, ANSES and published medical research.<\/p>\n\n\\n        \n\n<div class=\\\"yb-art-meta\\\">\\n          <img src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\\\" alt=\\\"Dr Alexandra Miles\\\">\\n          <span>By <strong>Dr Alexandra Miles<\/strong><\/span>\\n          <span>\u2022<\/span><span>Reviewed September 2026<\/span>\\n          <span>\u2022<\/span><span>15 min read<\/span>\\n        <\/div>\n\n\\n      <\/div>\n\n\\n    <\/div>\n\n\\n\\n    \n\n<div class=\\\"yb-art-layout\\\">\\n\\n      \n\n<div class=\\\"yb-art-body\\\">\\n\\n        \n\n<p>Vitamin C, or ascorbic acid, is the most widely taken vitamin supplement. It is water-soluble, the body stores very little of it and passes the excess out in the urine. That is what has earned it its reputation as a \\\"harmless\\\" vitamin. The reputation is largely deserved at dietary doses. It holds up less well with 1,000 mg tablets taken every day, effervescents taken by someone with high blood pressure, or infusions of several grams. <strong>Vitamin C side effects<\/strong> do exist. They depend on the dose, on the form, and above all on the person taking it. Here is what the data show, and what should make you measure before you supplement.<\/p>\n\n\\n\\n        \n\n<div class=\\\"yb-art-key\\\">\\n          \n\n<div class=\\\"yb-art-key-t\\\">Key takeaways<\/div>\n\n\\n          \n\n<p>From food alone, no vitamin C overdose has ever been described. With supplements, the MSD Manual puts the upper limit at <strong>2,000 mg a day<\/strong>: above it, nausea and diarrhoea are the most common <strong>side effects of vitamin C<\/strong>. The risk that really matters is renal: part of the vitamin C you take is converted into <strong>oxalate<\/strong>, which promotes <strong>kidney stones<\/strong> and, at very high doses, kidney damage. Two contraindications are firm: iron overload (haemochromatosis, thalassaemia) and, for high-dose infusions, <strong>G6PD deficiency<\/strong>. Effervescent tablets add sodium, a problem if your blood pressure is high. Before any long-term supplementation or any infusion, a <a href=\\\"\/en\/check-up\/medical-check-up\/\\\">blood test<\/a> measures your kidney function, blood sugar and blood count, <strong>at home and with no prescription needed<\/strong>.<\/p>\n\n\\n        <\/div>\n\n\\n\\n        \n\n<h2>Vitamin C: daily needs and the safety limit<\/h2>\n\n\\n        \n\n<p>Two figures frame vitamin C. On one side, the <strong>reference intake<\/strong>, the amount that covers the needs of a healthy adult. On the other, the <strong>tolerable upper intake level<\/strong> (UL), the total daily dose above which a risk of adverse effects can no longer be ruled out.<\/p>\n\n\\n        \n\n<p>For the reference intake, the French food safety agency ANSES sets <strong>110 mg a day<\/strong> for adults, 120 mg during pregnancy and 170 mg while breastfeeding. The MSD Manual quotes the US values, 75 mg for women and 90 mg for men, and adds that smokers need <strong>an extra 35 mg<\/strong> a day. One kiwi, one pepper or two oranges are enough to reach those amounts.<\/p>\n\n\\n        \n\n<p>For the upper limit, the situation is unusual. In its 2024 summary of tolerable upper intake levels, the European Food Safety Authority (EFSA) states for vitamin C: <strong>no adequate data to derive a UL<\/strong>. That is not a green light. It means no precise toxicity threshold could be set for lack of suitable studies, even though digestive effects and a risk of stones are documented. The US authorities, cited by the MSD Manual, set a practical limit at <strong>2,000 mg a day<\/strong>. That is the figure we use as our benchmark.<\/p>\n\n\\n        \n\n<div class=\\\"yb-art-tablewrap\\\">\\n          \n\n<table class=\\\"yb-art-table\\\">\\n            \n\n<thead>\n\n<tr>\n\n<th>Benchmark<\/th>\n\n\n\n<th>Adult value<\/th>\n\n\n\n<th>Source<\/th>\n\n<\/tr>\n\n<\/thead>\n\n\\n            \n\n<tbody>\\n              \n\n<tr>\n\n<td>Reference intake<\/td>\n\n\n\n<td><strong>110 mg\/day<\/strong> (120 mg pregnancy, 170 mg breastfeeding)<\/td>\n\n\n\n<td>ANSES<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td>Recommended intake (US values)<\/td>\n\n\n\n<td>75 mg women \/ 90 mg men, + 35 mg for smokers<\/td>\n\n\n\n<td>MSD Manual<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td>European upper limit<\/td>\n\n\n\n<td>Not set (insufficient data)<\/td>\n\n\n\n<td>EFSA 2024<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td>Practical upper limit<\/td>\n\n\n\n<td><strong>2,000 mg\/day<\/strong>, above it nausea and diarrhoea<\/td>\n\n\n\n<td>MSD Manual<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td>Blood level defining deficiency<\/td>\n\n\n\n<td>&lt; 0.2 mg\/dL (&lt; 11 \u00b5mol\/L)<\/td>\n\n\n\n<td>MSD Manual<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td>Standard pharmacy tablet<\/td>\n\n\n\n<td>500 to 1,000 mg, i.e. 5 to 9 times the reference intake<\/td>\n\n\n\n<td>Product labels<\/td>\n\n<\/tr>\n\n\\n            <\/tbody>\n\n\\n          <\/table>\n\n\\n        <\/div>\n\n\\n        \n\n<p class=\\\"yb-art-sources\\\">The Swiss reference values are published by the <a href=\\\"https:\/\/www.sge-ssn.ch\/de\/empfehlungen\/naehrstoffe-lebensmittel\/referenzwerte\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">Swiss Society for Nutrition<\/a> and the Federal Food Safety and Veterinary Office, based on the D-A-CH values.<\/p>\n\n\\n\\n        \n\n<h3>Can you overdose on vitamin C?<\/h3>\n\n\\n        \n\n<p>From food alone, no. You would need to eat several kilos of fruit a day to get anywhere near 2 grams. The picture changes with supplements. A single <strong>vitamin C 1,000 mg<\/strong> tablet is on its own nine times the reference intake. Two tablets, an \\\"immunity\\\" effervescent and a multivitamin, and you are past the 2,000 mg threshold without noticing. The MSD Manual notes that some people take up to <strong>10 g a day<\/strong> for benefits that have not been demonstrated.<\/p>\n\n\\n        \n\n<p>The term <strong>hypervitaminosis C<\/strong> is rarely used, because vitamin C does not build up in the tissues the way vitamins A or D do. <strong>Excess vitamin C<\/strong> shows itself differently: through what the surplus does on its way out, in the gut first, then in the kidneys. So the question is not \\\"is vitamin C dangerous?\\\", but \\\"at what dose, in what form, and with what kidneys?\\\".<\/p>\n\n\\n\\n        \n\n<h2>Vitamin C side effects: the symptoms of too much<\/h2>\n\n\\n\\n        \n\n<h3>Diarrhoea, nausea, bloating, heartburn: the digestive effects<\/h3>\n\n\\n        \n\n<p>This is the best-established side effect. According to the MSD Manual, taking <strong>more than 2 g of vitamin C a day<\/strong> can cause nausea and diarrhoea. The mechanism is simple: beyond a certain amount, the gut no longer absorbs everything, and the vitamin C left in the intestine draws in water. Hence the phrase \\\"vitamin C laxative effect\\\" that comes up online. Bloating, cramps, gas and loose stools often set in on the first or second day and disappear when you stop or lower the dose. If the diarrhoea lasts, it can dehydrate you, which is not a good state for your kidneys either. Vitamin C does not cause constipation: if you become constipated on a \\\"vitamin C + iron\\\" or \\\"vitamin C + calcium\\\" supplement, look at the other ingredient.<\/p>\n\n\\n        \n\n<p>Ascorbic acid is, as its name says, an acid. Taken on an empty stomach or as a pure powder, it can cause <strong>heartburn<\/strong>, stomach pain or make reflux worse. Taking it in the middle of a meal, or choosing a buffered form (sodium or calcium ascorbate), solves the problem in most cases. Be careful with sodium ascorbate if you watch your salt intake, which we come back to below.<\/p>\n\n\\n\\n        \n\n<h3>Does vitamin C make you sleepy or tired? Sleep, fatigue and headaches<\/h3>\n\n\\n        \n\n<p>\\\"Does ascorbic acid make you sleepy?\\\" and \\\"does vitamin C keep you awake?\\\" are two of the most searched questions, in opposite directions. The honest answer to both: no solid data show that vitamin C affects sleep, either way. Neither the MSD Manual nor EFSA describe such an effect. The impression probably comes from the products it is combined with (caffeine, guarana, \\\"energy\\\" complexes) or from a fizzy drink taken late in the evening. If in doubt, take your vitamin C in the morning: it changes nothing about absorption and removes the question.<\/p>\n\n\\n        \n\n<p>Likewise, \\\"too much vitamin C\\\" does not cause any documented fatigue. Persistent tiredness in someone who supplements should prompt a search for another cause, and often <a href=\\\"\/en\/expertise\/which-vitamin-deficiency-causes-fatigue\/\\\">the fatigue has a measurable explanation<\/a>: iron, thyroid, vitamin D, blood sugar. Mild headaches reported with high doses are possible but non-specific.<\/p>\n\n\\n\\n        \n\n<h3>Effects on the skin and face<\/h3>\n\n\\n        \n\n<p>Taken orally, vitamin C has no skin-related adverse effect described in the MSD Manual. The tingling, redness or irritation you read about under \\\"vitamin C for the face\\\" concern cosmetic serums applied to the skin, a dermatology topic separate from supplementation. The same goes for the \\\"skin whitening\\\" tablets sold in some countries: no lightening effect is documented, and the digestive and renal thresholds apply exactly as they do to any other tablet. If you want to know what vitamin C really does for the skin and the immune system, our article on <a href=\\\"\/en\/expertise\/what-are-the-benefits-of-vitamin-c\/\\\">the benefits of vitamin C<\/a> separates what is proven from what is not.<\/p>\n\n\\n\\n        \n\n<h2>Vitamin C, kidney stones and iron: the two real risks of overdose<\/h2>\n\n\\n\\n        \n\n<h3>Kidney stones and oxalate<\/h3>\n\n\\n        \n\n<p>This is the side effect of vitamin C that justifies medical caution. Part of the ascorbic acid is converted by the body into <strong>oxalate<\/strong>, then cleared by the kidneys. The MSD Manual notes that a high intake causes <strong>hyperoxaluria<\/strong> (excess oxalate in the urine) and thereby promotes the formation of <strong>calcium oxalate kidney stones<\/strong>, the most common type of stone. It adds that the acidification of the urine by vitamin C plays a part.<\/p>\n\n\\n        \n\n<p>At very high doses, the problem goes beyond stones. The medical literature describes cases of <strong>oxalate nephropathy<\/strong>: oxalate crystals settle in the kidney tubules and cause acute kidney failure. Two published cases set the orders of magnitude:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li>A 59-year-old woman whose kidney function had been normal two months earlier took <strong>more than 4 g of vitamin C a day for 30 days<\/strong> as part of an alternative treatment. She developed acute kidney failure with calcium oxalate deposits on biopsy, needed dialysis and did not recover her kidney function (Poulin et al., <em>Clinical Kidney Journal<\/em>, 2014).<\/li>\n\n\\n          \n\n<li>Two intensive care patients received <strong>112 g and 160 g of intravenous vitamin C<\/strong> over several days. Both developed oxalate nephropathy. The authors stress that pre-existing kidney damage and the dehydration of critical illness amplified the risk (Fontana et al., <em>Kidney International Reports<\/em>, 2020).<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>These cases are extreme and do not concern the person taking 500 mg in the morning. But they say one thing clearly: <strong>the kidney is the organ that limits vitamin C<\/strong>. A history of kidney stones, kidney failure even when mild, dehydration, bariatric surgery or a digestive disease that increases oxalate absorption: in these situations, high doses of vitamin C are to be avoided, and any high-dose infusion must be preceded by a measurement of kidney function. YuBoost's <a href=\\\"\/en\/check-up\/medical-check-up\/\\\">complete medical check-up<\/a> includes kidney function (creatinine, urea, filtration rate) among its 34 biomarkers, at home and with no prescription needed.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin C and iron: caution in iron overload<\/h3>\n\n\\n        \n\n<p>Vitamin C increases the intestinal absorption of non-haem iron, the iron found in plants. That is a useful property when you are short of iron: a glass of orange juice with your lentils improves uptake. It is a risk in the opposite situation. The MSD Manual states that in people with <strong>thalassaemia<\/strong> or <strong>haemochromatosis<\/strong>, a high vitamin C intake can worsen <strong>iron overload<\/strong>. Hereditary haemochromatosis often goes unnoticed for years and is picked up on a high ferritin found by chance.<\/p>\n\n\\n        \n\n<p>In other words, taking high-dose vitamin C for years without knowing your iron status is not trivial. <strong>Ferritin<\/strong>, transferrin and serum iron are among the 11 biomarkers of the <a href=\\\"\/en\/check-up\/vitamin-and-mineral-checkup\/\\\">vitamin and mineral check-up<\/a>. An unexplained high ferritin deserves a medical opinion before any supplementation, with vitamin C as much as with iron.<\/p>\n\n\\n\\n        \n\n<h2>Side effects by form: tablets, effervescents, liposomal, zinc + vitamin C<\/h2>\n\n\\n\\n        \n\n<h3>500 mg and 1,000 mg tablets and capsules<\/h3>\n\n\\n        \n\n<p>The most common form. One tablet a day stays below the 2,000 mg threshold. The <strong>side effects of vitamin C 1,000 mg tablets<\/strong> appear mostly when several products are combined, or in people with a sensitive digestion. The rule: add up every source (tablet, multivitamin, effervescent, fortified drink) before judging the dose. Taking vitamin C tablets daily for months is not a problem in itself for a healthy adult; it becomes one when the total creeps above 2 g, or when the kidneys or iron stores are not what you assume.<\/p>\n\n\\n\\n        \n\n<h3>Effervescent tablets: the sodium you cannot see<\/h3>\n\n\\n        \n\n<p>Effervescent tablets contain sodium bicarbonate or carbonate to make the bubbles. That dose of salt goes unnoticed, since nothing tastes salty. A case-control study published in the <em>BMJ<\/em> in 2013, covering more than 1.29 million patients in the United Kingdom, compared people taking effervescent, dispersible or soluble medicines containing sodium with people taking the same active ingredients in standard formulations. The result: a <strong>16%<\/strong> higher risk of a cardiovascular event (heart attack, stroke, vascular death), with an odds ratio of 1.16, and a risk of <strong>hypertension<\/strong> multiplied by 7 (odds ratio 7.18). The authors recommend prescribing sodium-containing forms with caution, and only when the expected benefit outweighs this risk.<\/p>\n\n\\n        \n\n<p>That study looked at medicines, not specifically at vitamin C, but the sodium is the same. If you have high blood pressure, heart failure or kidney failure, or if your doctor has asked you to cut down on salt, a daily effervescent is not the right form. A standard tablet delivers the same vitamin C without the sodium.<\/p>\n\n\\n\\n        \n\n<h3>Liposomal vitamin C<\/h3>\n\n\\n        \n\n<p>Liposomal vitamin C is ascorbic acid wrapped in phospholipids, sold on the promise of better absorption. On adverse effects, there are no specific data: the active molecule is the same, the digestive and renal thresholds apply in the same way, and if absorption really is better, so is the amount that reaches the kidneys. There is therefore no reason to regard the liposomal form as \\\"free of side effects\\\". The doses sold (often 1,000 mg per serving) count towards the daily total like any other.<\/p>\n\n\\n\\n        \n\n<h3>Zinc + vitamin C, vitamin C + calcium, acerola, powders<\/h3>\n\n\\n        \n\n<p>The digestive effects reported with the \\\"zinc + vitamin C\\\" supplements sold for immunity can come from either of the two ingredients. Before blaming the vitamin C, read the zinc dose on the label. The same applies to \\\"vitamin C + calcium\\\" products, where calcium is the more likely cause of constipation or bloating. For the combinations worth watching, see <a href=\\\"\/en\/expertise\/which-vitamins-cant-be-taken-together\/\\\">which vitamins can't be taken together<\/a>. Pure ascorbic acid powders, often measured out by the spoon, are the easiest form to overdose on: one level teaspoon is already several grams.<\/p>\n\n\\n\\n        \n\n<h2>High-dose intravenous vitamin C: side effects and contraindications<\/h2>\n\n\\n        \n\n<p>Taken orally, the gut caps what gets into the blood. With a <strong>vitamin infusion<\/strong>, that cap disappears: the whole dose enters the circulation, and the blood concentrations reached are on another scale from those of a tablet. At YuBoost, the <a href=\\\"\/en\/iv-therapy\/high-dose-vitamin-c\/\\\">High Dose Vitamin C<\/a> infusion delivers 7.5 g of vitamin C in about an hour, at home. It is offered <strong>on medical indication only<\/strong>, after an online consultation with a doctor and an individual assessment. Three points of vigilance explain that rule.<\/p>\n\n\\n\\n        \n\n<h3>G6PD deficiency: the risk of haemolysis<\/h3>\n\n\\n        \n\n<p>Glucose-6-phosphate dehydrogenase (G6PD) deficiency is, according to the MSD Manual, the most common disorder of red blood cell metabolism. It affects more than 10% of men of African descent and is common in populations from the Mediterranean basin (Italy, Greece, the Middle East) and from Asia. Most people who have it do not know: they are fine until the day an oxidising substance triggers a sudden destruction of red blood cells, <strong>haemolysis<\/strong>, with jaundice, dark urine, back pain and sometimes kidney injury.<\/p>\n\n\\n        \n\n<p>At very high doses, vitamin C behaves as an oxidant. A review published in 2022 in the <em>Indian Journal of Critical Care Medicine<\/em> gathered the <strong>14 published cases of haemolysis attributed to vitamin C<\/strong> between 1975 and 2020. Ten of them, <strong>71.4%<\/strong>, had G6PD deficiency. Doses ranged from 1 to 200 g a day, the intravenous route was involved in 57% of cases, and 11 of the 14 patients developed complications within <strong>3 days<\/strong> of starting treatment. Nearly half had acute kidney injury.<\/p>\n\n\\n        \n\n<p>The threshold is debated. In <em>Critical Care<\/em> in 2019, Paul Marik points out that the haemolysis cases involve very high pharmacological doses, above 60 g, and argues that 6 g a day should not be regarded as contraindicated in G6PD deficiency. Most clinical trials nonetheless exclude these patients as a precaution. Our position is simple: at 7.5 g per infusion, we do not take the risk blind. If you are of African, Mediterranean or Asian descent, or if you have ever had an unexplained episode of jaundice, a G6PD test is requested before any high-dose infusion.<\/p>\n\n\\n\\n        \n\n<h3>Kidney function and hydration<\/h3>\n\n\\n        \n\n<p>The oxalate nephropathy cases described above all involved high or repeated intravenous doses, often in patients whose kidneys were already weakened. <strong>Kidney failure<\/strong>, even when mild, and a history of <strong>kidney stones<\/strong> are contraindications to high-dose vitamin C. That is why kidney function is measured before the infusion, and why you are asked to drink well before and after.<\/p>\n\n\\n\\n        \n\n<h3>Diabetes: distorted glucose meter readings<\/h3>\n\n\\n        \n\n<p>A less well-known effect, but a documented one. After a high-dose vitamin C infusion, the blood concentration of ascorbic acid is high enough to interfere with strip-based glucose meters. A case published in 2013 in the <em>Journal of Diabetes Investigation<\/em> describes a diabetic patient who received 50 g of intravenous vitamin C: one meter showed severe hypoglycaemia, another major hyperglycaemia, while the laboratory assay gave a normal reading of 9.2 mmol\/L. The danger is injecting insulin, or glucose, on the basis of a false value. If you have insulin-treated diabetes, say so before any infusion: blood sugar is then checked in the laboratory, not on the meter, in the hours that follow.<\/p>\n\n\\n\\n        \n\n<h3>Mild effects possible during the infusion<\/h3>\n\n\\n        \n\n<p>The effects commonly reported with high-dose vitamin infusions remain modest: a feeling of warmth or thirst, discomfort at the needle site, passing nausea, needing to urinate more often in the following hours. They are monitored by the nurse on site. To find out what this route of administration can realistically deliver, read our analysis of <a href=\\\"\/en\/expertise\/the-effectiveness-of-intravenous-vitamin-infusions\/\\\">the effectiveness of intravenous vitamin infusions<\/a>.<\/p>\n\n\\n\\n        \n\n<div class=\\\"yb-art-quote\\\">\\n          \n\n<p>The question I ask before any high-dose vitamin C infusion is not \\\"do you want to boost your immunity?\\\" but \\\"how are your kidneys, and do you know your G6PD status?\\\". An infusion is prescribed on a blood test, never on a whim.<\/p>\n\n\\n          <cite>Dr Alexandra Miles, YuBoost<\/cite>\\n        <\/div>\n\n\\n\\n        \n\n<h2>Vitamin C and blood pressure, pregnancy, diabetes: the recurring questions<\/h2>\n\n\\n        \n\n<p><strong>Vitamin C and high blood pressure.<\/strong> Vitamin C does not raise blood pressure. A meta-analysis published in 2012 in the <em>American Journal of Clinical Nutrition<\/em>, pooling 29 randomised trials and 1,407 participants with a median dose of 500 mg a day, measured a modest fall in blood pressure: <strong>3.84 mmHg<\/strong> systolic and 1.48 mmHg diastolic, in short trials (8 weeks on median). The authors call for longer trials before drawing any recommendation. The only link between vitamin C and hypertension that should concern you is the sodium in effervescents, described above.<\/p>\n\n\\n        \n\n<p><strong>Vitamin C and pregnancy.<\/strong> Needs rise slightly (120 mg a day according to ANSES, 170 mg while breastfeeding) and are covered by a varied diet. EFSA has set no specific upper limit for pregnancy, for lack of data, which is a reason to stay within usual doses. High doses and infusions are not justified without medical advice during this period.<\/p>\n\n\\n        \n\n<p><strong>Vitamin C and diabetes.<\/strong> At usual oral doses, no demonstrated effect on blood sugar. The point of vigilance is the one described above: at very high doses, vitamin C distorts glucose meter readings, in one direction or the other depending on the device's technology.<\/p>\n\n\\n        \n\n<p><strong>Men and women.<\/strong> The side effects of vitamin C are the same in both sexes. The only difference in the references is the reference intake (75 mg for women versus 90 mg for men in the US values), which does not change the 2,000 mg threshold.<\/p>\n\n\\n\\n        \n\n<h2>Vitamin C contraindications: who should avoid it or ask a doctor<\/h2>\n\n\\n        \n\n<p>The <strong>contraindications of vitamin C<\/strong> come down to a few situations, mostly involving high doses and the intravenous route:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li><strong>History of kidney stones or kidney failure<\/strong>: avoid doses above the reference intake and any high-dose infusion without a prior measurement of kidney function (MSD Manual, published cases of oxalate nephropathy).<\/li>\n\n\\n          \n\n<li><strong>Haemochromatosis, thalassaemia, high ferritin<\/strong>: vitamin C worsens iron overload (MSD Manual). Have your ferritin measured before supplementing.<\/li>\n\n\\n          \n\n<li><strong>G6PD deficiency<\/strong>, known or suspected: contraindication to high-dose intravenous vitamin C, because of the risk of haemolysis. Usual oral doses are not concerned.<\/li>\n\n\\n          \n\n<li><strong>High blood pressure, heart failure, low-salt diet<\/strong>: avoid effervescent forms and sodium ascorbate, prefer a standard tablet.<\/li>\n\n\\n          \n\n<li><strong>Insulin-treated diabetes<\/strong>: no contraindication to vitamin C itself, but a laboratory blood sugar check after any high-dose infusion.<\/li>\n\n\\n          \n\n<li><strong>Long-term treatment<\/strong> (anticoagulant, chemotherapy, iron chelation): tell your doctor or pharmacist about any supplement, even a \\\"natural\\\" one.<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>For the other vitamins, some of which build up in the body and raise different problems, see <a href=\\\"\/en\/expertise\/what-are-the-risks-of-taking-too-many-vitamins\/\\\">what are the risks of taking too many vitamins<\/a> and, for the B group, <a href=\\\"\/en\/expertise\/what-are-the-side-effects-of-vitamin-b\/\\\">the side effects of vitamin B<\/a>.<\/p>\n\n\\n\\n        \n\n<h2>Too much vitamin C: the overdose symptoms that should alert you<\/h2>\n\n\\n        \n\n<p>If you take a vitamin C supplement and recognise yourself in any of these signs, do not increase the dose, and see a doctor:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li>Diarrhoea, nausea or abdominal cramps that last more than a few days;<\/li>\n\n\\n          \n\n<li>Sudden pain in the lower back or flank, radiating towards the groin, blood in the urine (signs of a kidney stone);<\/li>\n\n\\n          \n\n<li>Passing less urine, swollen legs, unusual tiredness after a high dose or an infusion (renal signs);<\/li>\n\n\\n          \n\n<li>Jaundice, very dark urine, breathlessness, back pain in the days after a high-dose infusion (signs of haemolysis, emergency);<\/li>\n\n\\n          \n\n<li>Blood pressure that has been climbing since you switched to a daily effervescent;<\/li>\n\n\\n          \n\n<li>Swelling of the face or lips, hives, difficulty breathing (allergic reaction, rare but possible with any supplement, emergency).<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>Conversely, slightly yellower urine or needing to urinate more often after a high dose are not signs of overdose. That is the surplus leaving the body.<\/p>\n\n\\n\\n        \n\n<h2>Should you have a blood test before taking vitamin C?<\/h2>\n\n\\n        \n\n<p>Not for the occasional tablet during a cold. Yes, as soon as the intake becomes daily and prolonged, the dose exceeds 1,000 mg, or a high-dose infusion is being considered. The logic is the same as for any supplement: you only correct what is missing, and you check that the body can handle what you give it. A genuine <strong>vitamin C deficiency<\/strong> shows up in a blood test (a level below 0.2 mg\/dL according to the MSD Manual) and is treated with 500 to 1,000 mg a day for one to two weeks, not with grams for years. To recognise the signs of a shortfall, <a href=\\\"\/en\/expertise\/how-can-you-tell-if-you-have-a-vitamin-deficiency\/\\\">how can you tell if you have a vitamin deficiency<\/a> gives you the pointers; to know when supplementing makes sense, read <a href=\\\"\/en\/expertise\/in-what-cases-should-vitamin-c-be-taken\/\\\">in what cases vitamin C should be taken<\/a>.<\/p>\n\n\\n        \n\n<p>YuBoost's <a href=\\\"\/en\/check-up\/medical-check-up\/\\\">complete medical check-up<\/a> measures <strong>34 biomarkers<\/strong>, including <strong>kidney function<\/strong>, blood count, blood sugar, liver, thyroid and inflammation: exactly what determines whether a vitamin C supplement or infusion is safe for you. How it works:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li><strong>Blood draw at home<\/strong> by a registered nurse, <strong>no prescription needed<\/strong>, in Lausanne, Geneva, Zurich and across French-speaking Switzerland;<\/li>\n\n\\n          \n\n<li><strong>Analysis in an accredited Swiss laboratory<\/strong>, results within 7 working days;<\/li>\n\n\\n          \n\n<li><strong>Personalised medical report<\/strong> and an optional online consultation with a doctor.<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>The check-up costs <strong>CHF 350<\/strong>. If your question is about iron, the <a href=\\\"\/en\/check-up\/vitamin-and-mineral-checkup\/\\\">vitamin and mineral check-up<\/a> (CHF 370) measures ferritin, transferrin and iron along with eight other markers. When a deficiency is confirmed or a medical indication is established, a <a href=\\\"\/en\/expertise\/what-exactly-are-vitamin-c-injections\/\\\">vitamin C injection<\/a> or the <a href=\\\"\/en\/iv-therapy\/high-dose-vitamin-c\/\\\">High Dose Vitamin C<\/a> infusion (7.5 g, CHF 450) can be offered, at home, after assessment by a doctor. For the full picture of the vitamin itself, roles, needs, food sources and routes of administration, see our <a href=\\\"\/en\/vitamins\/vitamin-c\/\\\">vitamin C guide<\/a>. Vitamin C side effects are not inevitable: they are a matter of dose, form and individual terrain, and the only way to avoid them is to know yours before you start.<\/p>\n\n\\n\\n        \n\n<h2>Frequently asked questions<\/h2>\n\n\\n        \n\n<div class=\\\"yb-art-faq\\\">\\n          \n\n<details open>\n\n<summary>What are the side effects of vitamin C?<\/summary>\n\n\n\n<p>At dietary doses, none. With supplements, the effects documented by the MSD Manual are nausea and diarrhoea above 2,000 mg a day, and an increase in urinary oxalate that promotes kidney stones. In people with haemochromatosis or thalassaemia, vitamin C worsens iron overload. Effervescent forms add sodium, a problem in case of high blood pressure.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>What happens if you take too much vitamin C?<\/summary>\n\n\n\n<p>Most of the surplus is passed out in the urine, which explains the absence of acute toxicity at usual doses. Above 2 g a day, the gut can no longer keep up and diarrhoea appears. Over time, or at very high doses, the kidney takes the hit: calcium oxalate stones and, in published cases from 4 g a day for a month, acute kidney failure.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Do vitamin C 1,000 mg tablets have side effects?<\/summary>\n\n\n\n<p>One 1,000 mg tablet a day stays below the 2,000 mg upper limit set by the US authorities and cited by the MSD Manual. Digestive effects appear mostly when several products are combined or in sensitive people. If you have a history of kidney stones or a high ferritin, even 1,000 mg a day over the long term deserves a medical opinion.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Does vitamin C cause kidney stones?<\/summary>\n\n\n\n<p>It increases the risk at high doses. Part of the vitamin C is converted into oxalate, and the MSD Manual states that a high intake promotes calcium oxalate stones. The risk is greater in people who have already had stones, in kidney failure or in dehydration. These people should stick to the reference intake.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Does ascorbic acid make you sleepy, or keep you awake?<\/summary>\n\n\n\n<p>Neither is supported by scientific data, and neither the MSD Manual nor EFSA describe an effect on sleep or alertness. The impression often comes from the products it is combined with (caffeine, \\\"energy\\\" complexes). If in doubt, take vitamin C in the morning: its absorption does not depend on the time of day.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Do effervescent vitamin C tablets have specific side effects?<\/summary>\n\n\n\n<p>Yes, because of the sodium they contain to produce the bubbles. A 2013 <em>BMJ<\/em> study of 1.29 million patients linked sodium-containing effervescent and soluble medicines to a 16% higher cardiovascular risk and a sevenfold higher risk of hypertension compared with the same active ingredients in standard tablets. If you have high blood pressure or follow a low-salt diet, choose a non-effervescent tablet.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>What are the side effects of intravenous vitamin C?<\/summary>\n\n\n\n<p>Mild effects (warmth, thirst, discomfort at the needle site, passing nausea) are common and harmless. The serious risks concern specific profiles: haemolysis in G6PD deficiency (10 of the 14 published cases), oxalate nephropathy in kidney failure, and distorted glucose meter readings in diabetics. That is why a high-dose infusion is given on medical indication only, after a blood test.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>How do I know whether I can take vitamin C safely?<\/summary>\n\n\n\n<p>By checking three things: your kidney function, your ferritin and, before a high-dose infusion, your G6PD status. YuBoost's complete medical check-up measures kidney function, blood sugar and blood count among 34 biomarkers, at home and with no prescription needed in Lausanne, Geneva, Zurich and across French-speaking Switzerland, with results interpreted by a doctor.<\/p>\n\n<\/details>\n\n\\n        <\/div>\n\n\\n\\n        \n\n<h2>Sources<\/h2>\n\n\\n        \n\n<p class=\\\"yb-art-sources\\\">\\n          \u2022 MSD Manual Professional Edition, <em>Vitamin C Toxicity<\/em> (2,000 mg\/day upper limit, nausea and diarrhoea, hyperoxaluria and stones, iron overload): <a href=\\\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/vitamin-c-toxicity\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 MSD Manual Professional Edition, <em>Vitamin C Deficiency<\/em> (recommended intakes, smokers, deficiency threshold, treatment): <a href=\\\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/vitamin-c-deficiency\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 MSD Manual Professional Edition, <em>Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency<\/em> (prevalence, populations, triggers, symptoms): <a href=\\\"https:\/\/www.msdmanuals.com\/professional\/hematology-and-oncology\/anemias-caused-by-hemolysis\/glucose-6-phosphate-dehydrogenase-g6pd-deficiency\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 EFSA, <em>Summary of Tolerable Upper Intake Levels<\/em>, 2024 version (vitamin C: no adequate data to derive a UL): <a href=\\\"https:\/\/www.efsa.europa.eu\/sites\/default\/files\/2024-05\/ul-summary-report.pdf\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 ANSES, <em>Dietary reference values for vitamins and minerals<\/em> (vitamin C: 110 mg\/day adults, 120 mg pregnancy, 170 mg breastfeeding): <a href=\\\"https:\/\/www.anses.fr\/en\/content\/dietary-reference-values-vitamins-and-minerals\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Poulin L.-D. et al., <em>Acute oxalate nephropathy induced by oral high-dose vitamin C alternative treatment<\/em>, Clinical Kidney Journal, 2014: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC3970339\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Fontana F. et al., <em>Oxalate Nephropathy Caused by Excessive Vitamin C Administration in 2 Patients With COVID-19<\/em>, Kidney International Reports, 2020: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC7363608\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Juneja D., Jain R., Nasa P., <em>Vitamin C-induced Hemolysis: Meta-summary and Review of Literature<\/em>, Indian Journal of Critical Care Medicine, 2022: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC8857720\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Marik P. E., <em>Is intravenous vitamin C contraindicated in patients with G6PD deficiency?<\/em>, Critical Care, 2019: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC6448313\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Kimura T. et al., <em>Pseudohypoglycemia or hyperglycemia caused by interference with self-monitoring blood glucose measurements in anticancer ascorbic acid therapy<\/em>, Journal of Diabetes Investigation, 2013: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC4020267\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 George J. et al., <em>Association between cardiovascular events and sodium-containing effervescent, dispersible, and soluble drugs: nested case-control study<\/em>, BMJ, 2013: <a href=\\\"https:\/\/discovery.dundee.ac.uk\/en\/publications\/association-between-cardiovascular-events-and-sodium-containing-e\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Juraschek S. P. et al., <em>Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials<\/em>, American Journal of Clinical Nutrition, 2012: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC3325833\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Swiss Society for Nutrition SSN, <em>Referenzwerte f\u00fcr die N\u00e4hrstoffzufuhr<\/em> (reference values, in German): <a href=\\\"https:\/\/www.sge-ssn.ch\/de\/empfehlungen\/naehrstoffe-lebensmittel\/referenzwerte\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a>\\n        <\/p>\n\n\\n\\n      <\/div>\n\n\\n\\n      \n\n<aside class=\\\"yb-art-aside\\\">\\n        \n\n<div class=\\\"yb-art-panel yb-art-panel--cta\\\">\\n          \n\n<div class=\\\"k\\\">Take action<\/div>\n\n\\n          \n\n<h3>Check your <em>kidneys<\/em> before high-dose vitamin C<\/h3>\n\n\\n          \n\n<p>Kidney function, blood sugar, blood count, liver, thyroid: 34 biomarkers. At home, no prescription needed, across French-speaking Switzerland.<\/p>\n\n\\n          <a class=\\\"yb-art-sbtn yb-art-sbtn--p\\\" href=\\\"\/en\/booking\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=cta-side\\\">Book an appointment<\/a>\\n          <a class=\\\"yb-art-sbtn yb-art-sbtn--g\\\" href=\\\"\/en\/check-up\/medical-check-up\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=cta-side-checkup\\\">See the check-up: CHF 350<\/a>\\n        <\/div>\n\n\\n        <a class=\\\"yb-art-panel yb-art-panel--author\\\" href=\\\"\/en\/about-us\/\\\">\\n          <img src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\\\" alt=\\\"Dr Alexandra Miles\\\">\\n          \n\n<div><strong>Dr Alexandra Miles<\/strong><span>CEO YuBoost \u00b7 Functional medicine<\/span><\/div>\n\n\\n        <\/a>\\n      <\/aside>\n\n\\n\\n    <\/div>\n\n\\n  <\/div>\n\n\\n\\n  \n\n<div class=\\\"yb-rel\\\">\\n    \n\n<div class=\\\"yb-rel__head\\\">\\n      <span class=\\\"yb-art-eyebrow\\\">Go further<\/span>\\n      \n\n<h2>Measure before you supplement<\/h2>\n\n\\n      \n\n<p>At home across French-speaking Switzerland, no prescription needed.<\/p>\n\n\\n    <\/div>\n\n\\n    \n\n<div class=\\\"yb-rel__viewport\\\">\\n      <button type=\\\"button\\\" class=\\\"yb-rel__nav yb-rel__nav--prev\\\" aria-label=\\\"Previous\\\"><svg viewBox=\\\"0 0 24 24\\\" fill=\\\"none\\\" stroke=\\\"currentColor\\\" stroke-width=\\\"2\\\" aria-hidden=\\\"true\\\"><path d=\\\"M15 18l-6-6 6-6\\\"\/><\/svg><\/button>\\n      \n\n<div class=\\\"yb-rel__track-wrap\\\">\\n        \n\n<div class=\\\"yb-rel__track\\\">\\n\\n          <a class=\\\"yb-rel__card yb-rel__card--featured\\\" href=\\\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=rel-checkup\\\">\\n            <span class=\\\"yb-rel__badge yb-rel__badge--top\\\">Most relevant<\/span>\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/04\/bilan-sanguin-complet.png\\\" alt=\\\"Complete medical check-up with kidney function, at home in Switzerland, before vitamin C supplementation\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Complete check-up<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Complete medical check-up<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">34 biomarkers: kidney function, blood sugar, blood count, liver, thyroid, inflammation. At home.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">Kidney function<\/span><span class=\\\"yb-rel__chip\\\">34 markers<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">CHF 350<\/span><span class=\\\"yb-rel__cta\\\">Book<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n          <a class=\\\"yb-rel__card\\\" href=\\\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=rel-vitamins\\\">\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/06\/Bilan-vitamines.png\\\" alt=\\\"Vitamin and mineral check-up with ferritin and iron testing at home in Switzerland\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Deficiencies &amp; iron<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Vitamin &amp; mineral check-up<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">Iron, ferritin, transferrin, vitamins B6, B9, B12 and D, magnesium, calcium, zinc. At home.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">Ferritin<\/span><span class=\\\"yb-rel__chip\\\">11 markers<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">CHF 370<\/span><span class=\\\"yb-rel__cta\\\">Book<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n          <a class=\\\"yb-rel__card\\\" href=\\\"https:\/\/yuboost.com\/en\/iv-therapy\/high-dose-vitamin-c\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=rel-highdose\\\">\\n            <span class=\\\"yb-rel__badge yb-rel__badge--new\\\">On medical indication<\/span>\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/03\/HighDoseVitaminC.png\\\" alt=\\\"High-dose vitamin C infusion at home in Switzerland, on medical indication\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Vitamin infusion<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">High Dose Vitamin C<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">Vitamin C 7.5 g. After a blood test and medical consultation, at home, about 60 minutes.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">7.5 g<\/span><span class=\\\"yb-rel__chip\\\">60 min<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">CHF 450<\/span><span class=\\\"yb-rel__cta\\\">Discover<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n          <a class=\\\"yb-rel__card\\\" href=\\\"https:\/\/yuboost.com\/en\/vitamins\/vitamin-c\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=rel-vitamin-c\\\">\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/04\/EN-Vitamin-C-e1776841839202.png\\\" alt=\\\"Vitamin C guide: roles, needs, deficiency and routes of administration, YuBoost Switzerland\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Vitamin C<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Vitamin C guide<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">The complete guide: roles, needs, deficiency, food sources and routes of administration.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">Guide<\/span><span class=\\\"yb-rel__chip\\\">At home<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">Discover<\/span><span class=\\\"yb-rel__cta\\\">View<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n        <\/div>\n\n\\n      <\/div>\n\n\\n      <button type=\\\"button\\\" class=\\\"yb-rel__nav yb-rel__nav--next\\\" aria-label=\\\"Next\\\"><svg viewBox=\\\"0 0 24 24\\\" fill=\\\"none\\\" stroke=\\\"currentColor\\\" stroke-width=\\\"2\\\" aria-hidden=\\\"true\\\"><path d=\\\"M9 18l6-6-6-6\\\"\/><\/svg><\/button>\\n    <\/div>\n\n\\n    \n\n<div class=\\\"yb-rel__dots\\\"><\/div>\n\n\\n  <\/div>\n\n\\n\\n  \n\n<div class=\\\"yb-art-container\\\">\\n    \n\n<div class=\\\"yb-art-cta\\\">\\n      \n\n<div class=\\\"yb-art-cta-blob\\\"><\/div>\n\n\\n      \n\n<div class=\\\"yb-art-cta-in\\\">\\n        <span class=\\\"yb-art-eyebrow\\\">Take action<\/span>\\n        \n\n<h2>Measure before you <span class=\\\"yb-art-accent\\\">supplement<\/span><\/h2>\n\n\\n        \n\n<p class=\\\"yb-art-cta-sub\\\">Kidney function, blood sugar, blood count, liver and thyroid in a single check-up, at home across French-speaking Switzerland and with no prescription needed. Blood draw by a registered nurse, results interpreted by a doctor. The high-dose vitamin C infusion comes only after.<\/p>\n\n\\n        <a class=\\\"yb-art-btn\\\" href=\\\"\/en\/booking\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=cta-final\\\">Book an appointment<\/a>\\n        <a class=\\\"yb-art-btn-ghost\\\" href=\\\"\/en\/check-up\/medical-check-up\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-c-side-effects&amp;utm_content=cta-final-checkup\\\">See the check-up: CHF 350<\/a>\\n      <\/div>\n\n\\n    <\/div>\n\n\\n    \n\n<p class=\\\"yb-art-disc\\\">This article is for information only and does not replace individual medical advice. In case of sudden lower back pain, blood in the urine, jaundice or an allergic reaction after taking vitamin C, consult a healthcare professional. Reviewed by Dr Alexandra Miles, September 2026.<\/p>\n\n\\n  <\/div>\n\n\\n\\n<\/div>\n\n\"}}]}]}]}],\"version\":\"5.0.46\",\"yooessentialsVersion\":\"3.0.15\"} --><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Home \u203a Our articles \u203a Vitamin C side effects Vitamins &amp; safety Vitamin C side effects, overdose and contraindications 1,000 mg tablets, effervescents, liposomal vitamin C, high-dose infusions: which side effects of vitamin C are real, from what dose, and who should avoid it. A review based on the MSD Manual, EFSA, ANSES and published [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":41762,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[80],"tags":[],"class_list":["post-31714","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-expertise"],"acf":[],"_links":{"self":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts\/31714","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/comments?post=31714"}],"version-history":[{"count":5,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts\/31714\/revisions"}],"predecessor-version":[{"id":41767,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts\/31714\/revisions\/41767"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/media\/41762"}],"wp:attachment":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/media?parent=31714"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/categories?post=31714"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/tags?post=31714"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}